Tetanus doesn’t grab many headlines these days. In this era of superbugs and COVID-19, a disease that can be prevented by vaccination and sensible wound management might seem almost tame.
But tetanus is anything but. Cases may not be as common as they once were, but this disease still poses a mortal threat to horses and humans alike. Clostridium tetani is an anaerobic organism, meaning it thrives in moist, low oxygen conditions. So if the environment is right in a wound contaminated with C. tetani spores, the bacteria are activated, multiply and release powerful neurotoxins that cause painful muscle contraction and spasms. Often the muscles of the head and neck are among the most obviously affected, which is why tetanus is commonly called “lockjaw.” Horses with the disease often adopt a characteristic “sawhorse” stance, as well, as muscles in the back and torso seize. More than 50 percent of horses who contract tetanus die or must be euthanatized.
Thanks to vaccination, tetanus is rare among America’s horses, but it does occur. “I wish there were zero cases,” says Simon Peek, BVSc, MRCVS, PhD, DACVIM, of the University of Wisconsin-Madison. “It’s such a horrible disease that we’d prefer to never see it again. Yet we continue to have sporadic cases, and it’s always tragic when we do.”
So you are unlikely to ever see a case of tetanus firsthand, but you’ll still want to take the threat seriously. The frontline of defense is vaccination ---it’s easy, effective and inexpensive. Beyond that, it’s wise to become familiar enough with tetanus to understand when horses are most at risk and why. To help you, we’ve provided an overview (see “In Focus: Tetanus,” page 30) along with the following collection of lesser known facts about this deadly disease.
1. HORSES ARE PARTICULARLY SUSCEPTIBLE.
Horses are at higher risk of developing tetanus than other animals. First, as a species, horses are unusually vulnerable to the C. tetani infection---a relatively small amount of the toxins produced by the pathogen can be deadly. In contrast, chickens and other birds are highly resistant---a lethal dose is up to 300,000 higher per pound of body weight than for a horse. Likewise, it takes a fairly high dose of toxin to cause dogs and cats to develop tetanus.
Second, horses are very likely to be exposed to C. tetani. The organism’s spores are widespread in the environment; the soil in most regions is contaminated with them. C. tetani spores are often present in the digestive tract of animals, as well. “These soil bacteria can become part of normal flora in the horse’s intestine and are therefore present in manure,” explains Nat Messer, DVM, DABVP, professor emeritus of the University of Missouri. When deposited on the ground, the bacteria go dormant and can survive almost indefinitely.
Finally, many cuts, abrasions and other wounds occur on the very areas of the horse’s body where the risk of exposure to C. tetani is highest and where conditions are right for the organism to flourish: the lower legs. Because it is anaerobic, C. tetani cannot thrive in healthy, oxygen-rich tissues, so the horse’s lower limbs, which are not well-oxygenated to begin with, would provide a welcoming environment. In contrast, tetanus is less likely to develop from wounds to larger muscle groups elsewhere on the body that are well supplied with blood.
2. VIRTUALLY ANY WOUND—NOT JUST PUNCTURES—CAN LEAD TO TETANUS.
In the classically imagined tetanus scenario, a horse steps on a rusty nail that pushes C. tetani spores deep into the resulting puncture wound, where the bacteria multiply and ultimately release the toxins that cause disease. In reality, though, tetanus can result from virtually any break in the skin that allows C. tetani spores to enter the body. In fact, health officials warn that superficial wounds that may be overlooked or less carefully cleaned pose an outsized tetanus risk compared to punctures or more severe injuries likely to receive prompt and thorough medical attention.
Tetanus is also a postpartum risk for mares and for their newborn foals. “Mares after foaling can develop tetanus from contamination of the uterus, and foals are at risk via umbilical infections---though these cases are less common than from puncture wounds,” says Messer.
Lastly, tetanus can occur after surgery, although modern veterinary practices have pretty much eliminated this threat. “Most veterinarians are fastidious about proper surgical technique and cleanliness,” says Peek, “and prior to doing procedures such as castration they make sure that the horse has had appropriate tetanus vaccination.”
REDUCE YOUR HORSE’S RISK
In addition to vaccination, there are several things you can do to protect your horse from tetanus—mainly reducing his risk of injury and taking proper care of those wounds that do inevitably occur.
• Pick up debris and minimize sharp edges in your horse’s environment. It seems inevitable that if there’s a single nail on the ground, sooner or later it will end up in a horse’s foot. Try to pick up all stray nails and other debris after farrier visits as well as after construction or repair work around the farm. Also inspect fences, stalls and other structures to find and repair loose nails, splinters or other sharp projections that may cause injury. “Continually scrutinize the safety of the horses’ environment because if there is anything unsafe, they will find it sooner or later and get hurt,” says Nat Messer, DVM, DABVP, professor emeritus of the University of Missouri.
• Clean all wounds, no matter how small. Even very tiny wounds can lead to problems. Take time to cleanse all wounds: Rinse away any dirt or debris, and consider a quick wash with a topical disinfectant. “If the horse has been vaccinated and gets a small wound that the owner is capable of treating, they don’t have to worry about having a veterinarian come out to give a tetanus shot,” Messer says. “The horse is protected.”
• Take puncture wounds seriously. Deeper wounds that close over at the surface are more likely to harbor serious infections under the skin. Wounds on the lower legs and hooves, which are more likely to be exposed to dirt and manure, are even more vulnerable.
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